1. Field of the Invention:
This invention relates to systems for reproducing color images by scanning an original and using electrical signals from the scanner to control the paint-spraying of a larger duplicate image. More particularly the invention relates to an improvement in the construction of the spray head and in the method and construction of the ink supply.
2. Description of Related Art:
Systems have been in use for making enlarged prints, such as for billboards, in which an original image is scanned to produce control signals that operate the reproduction equipment. One such system is described in U.S. Pat. No. 1,709,926 in which the original and the recording medium are each carried by a rotating cylinder. A color duplicate of the original is produced by mechanically controlling three ink jets in accordance with signals produced by scanning the original while the ink jets are moved slowly across the width of the recording medium.
U.S Pat. No. 1,817,098 describes a facsimile system using a first drum for scanning and a second drum for recording. The initial signal is divided into color components from which electrical control signals are generated. The control signals cause electric potentials to be applied to a pair of deflection electrodes positioned on opposite sides of a stream of atomized ink particles so that the ink stream is deflected toward the recording medium when an electrical potential is applied to the electrodes. When no voltage is present on the electrodes, the ink spray is prevented from reaching the recording medium.
U.S. Patent No. 3,553,371 describes another dual-cylinder system in which multi-color images are reproduced by using one or more ink-jet heads operated in synchronism with the scanning signals. The pressure of the air is amplitude modulated in accordance with the scanner signals and the modulated air controls a mechanical valve that regulates the rate of ink flow The extent to which the ink valve is opened is a function of the air pressure. The same patent also describes spray heads in which the ink jet is controlled by a mechanical valve operated directly by the scanner signals without pressure modulation of the air stream.
Jets that include a mechanical ink valve operated by the recording signals are slow and suffer from problems associated with contamination, clogging and wear of the valve mechanism. Various attempts to amplitude modulate the air stream and avoid the problems associated with variable ink valves have not been commercially successful, in part because the character of the atomized ink is a function of the pressure of the air that produces the ink spray.